(1) Field of the Invention
The present invention relates to an actuator which is used for a robot or the like to cause relative displacement between two bodies. More particularly, the present invention relates to an actuator fabricated by using a shape memory alloy. Furthermore, the present invention relates to an articulated arm for a robot or the like, which comprises this actuator.
(2) Description of the Related Art
A robot moving on a wall surface of a building, a conduit or a cable, unlike a robot moving on the ground, should always move while assuming a correct posture thereof. Accordingly, an actuator used for an articulated arm of this moving robot is required to have a high output and a high torque. In general, however, as the output and torque increase, the weight of the actuator proportionally increases. Ideally, an actuator having such a high output/weight ratio as that of the muscle of a man is desirable.
Actuators heretofore used for robots or the like are mainly servo motors, hydraulic cylinders and pneumatic cylinders, and in these actuators, the output/weight ratios are much lower than that of the human muscle and from the viewpoint of the efficiency, these actuators are not adequate as the actuator for a moving robot.
Investigations have recently been made to reduce the size and weight of an actuator and simplify the mechanism by using a shape memory alloy (hereinafter referred to as "SMA") which is a dynamic mechanical material (see, for example, Japanese Patent Application Laid-open Specification No. 61-177179, No. 61-84427, No. 62-77882 and 63-57977). However, most of these investigations are directed to the use of linear or coil springtype SMA, and even if the output/weight ratio is improved, there arises a problem as regards the space occupied by the mechanism).